From The Serpent's Pass:
Aang: I don't know. The monks used to say that hope was just a distraction, so maybe we do need to abandon it.
Katara: What are you talking about?
Aang: Hope is not going to get us into Ba Sing Se and it's not going to help find Appa. We need to focus on what we're doing right now and that's getting across this path.
I've never understood this. Why exactly were the Air Nomads against the concept of hope? How would hope distract them? Wouldn't hope for a specific goal help them achieve that goal?
Additionally, Aang seems pretty hopeful for most of the series. The Air Nomads also seemed to have hope for lots of things. For example, they hoped that Aang would help deal with the Fire Nation's aggression.
Later Aang abandons this ideal and it's never brought up again.
Aang: [Sheds some tears.] I've been going through a really hard time lately. But you've made me ... hopeful again.
Are there any in-universe or out-of-universe explanations for this aspect of Air Nomad culture?